Roentgen discovered X-radiation by the inadvertent exposure of a silver halide photographic element. In 1913, Eastman Kodak Company introduced its first product specifically intended to be exposed by X-radiation (X-rays). Silver halide radiographic films account for the overwhelming majority of medical diagnostic images. It was recognized almost immediately that the high energy ionizing X-rays are potentially harmful and ways were sought to avoid high levels of patient exposure. Radiographic films provide viewable silver images upon imagewise exposure followed by rapid access processing.
One approach, still in wide-spread use is to coat the silver halide emulsions useful in radiographic films on both sides of the film support. Thus, the number of X-rays that can be absorbed and used for imaging are doubled, providing higher sensitivity. Dual-coated radiographic films are sold by Eastman Kodak Company under the trademark DUPLITIZED films. Films that rely entirely on X-radiation absorption for image capture are referred to in the art as "direct" radiographic elements, while those that rely on intensifying screen light emission are referred to as "indirect" radiographic elements.
There are other applications for direct radiographic films, such as in various industrial applications where X-rays are captured in imaging, but intensifying screens cannot be used for some reason (such as for pipeline and turbine blade welds).
It is the prevailing practice to process radiographic films using black-and-white development, fixing, washing and drying. Films processed in this manner are then ready for image viewing.
Photographic black-and-white developing compositions containing a silver halide black-and-white developing agent are well known in the photographic art for reducing silver halide grains containing a latent image to yield a developed photographic image. Many useful developing agents are known in the art, with hydroquinone and similar dihydroxybenzene compounds and ascorbic acid (and derivatives) being some of the most common. Such compositions generally contain other components such as sulfites, buffers, antifoggants, halides and hardeners.
Fixing compositions for radiographic films are also well known and include one or more fixing agents, of which thiosulfates are most common. Such compositions generally include sulfites as antioxidants.
U.S. Pat. No. 5,800,976 (Dickerson et al) describes radiographic elements having lower silver coverage and including certain covering power enhancing compounds within the silver halide emulsions. Such elements are generally processed in conventional developing compositions that include hydroquinone or other dihydroxybenzene compounds. However, such developing compositions are not desirable because of their negative impact on the environment. "Monobath" solutions are also known in the art of photographic processing. These solutions typically require long processing times and contain components common to both developing and fixing compositions, that is a high pH and sulfite. It has been difficult to achieve acceptable processing with monobath solutions because either fixing occurred too quickly (thus D.sub.max is too low) or little fixing occurred because of fogging (high D.sub.min) or there was too little fixing agent or insufficient fixing time. The desired balance of all conditions and sensitometric results is difficult to achieve. Either very long processing time is needed, or the density is too low from removal of too much silver. These concerns are increased when the radiographic elements to be processed contain silver coverage that is lower than normal.
Various two-stage processing methods have been carried out using roomlight handleable radiographic elements such as those described in U.S. Pat. No. 5,871,890 (Fitterman et al). While those methods are useful in the specific contexts described in the noted applications, there is no appreciation that two-stage processing could be used effectively with radiographic element containing reduced silver coverage.
The industry needs a two-stage processing method that overcomes the noted problems and can provide acceptable black-and-white images in a short time in an environmentally acceptable manner.